The proposed studies will provide information essential for understanding the mechanisms that underlie: 1) processes of sensory information transfer from the dorsal root ganglion (DRG) neuron to the dorsal horn (DH) neuron, and 2) sensory signal modulation at the DH level of the first synapse by opioids. The methodology involved includes using an unique spinal cord slice preparation that consists of a spinal dorsal horn slice with attached dorsal root and DRG obtained from 20-30 day old rats. This unique preparation will enable us to perform simultaneous intracellular recordings from the DRG and DH neurons. Changes in resting membrane potentials evoked by primary afferent fiber activation will be recorded as an indicator of synaptic transmission. By utilizing the advantages of an in vitro preparation with completely preserved synaptic interactions, we will investigate the relationship between the physiology and morphology of superficial DH neurons. By changing the concentration of Ca ion in the recording solution, we will establish which portion of the DR-evoked response is polysynaptic and hope to establish the correlation between the DH neuron dendritic spread and the monosynaptic input. By stimulating one or several DR we will study the type of interaction of postsynaptic potentials on single DH neuron. Furthermore, the types of integration of synaptic potentials will be examined in the presence of inhibitory transmitter antagonists (naloxone and bicuculline). Employment of specific excitatory amino acid receptor antagonists will establish the correlation between putative transmitters and synaptic potentials. In addition, the simultaneous recording from DRG neurons and synaptically coupled DH neurons will allow the analysis of unitary postsynaptic potentials and the establishment of the nature of the transmitter(s) released from primary afferent fibers. Furthermore, the site and mechanism of opioid inhibitory action on the transmission of information in the DH will be studied.